1. Field of the Invention
The present invention relates to an LCD (liquid crystal display) apparatus, and more particularly to an LCD apparatus that can display images in different video formats of different sizes (pixel configurations).
2. Description of the Prior Art
LCD panels are available in different pixel configurations for different video formats such as XGA, SVGA, and VGA. The numbers of columns and rows of pixels that these LCD panels can display are as follows:
XGA 1,024 .times. 768 pixels SVGA 800 .times. 600 pixels VGA 640 .times. 480 pixels
On the other hand, images to be displayed on an LCD panel are generally produced on a personal computer, which can output images in any of XGA, SVGA, and VGA formats depending on the video mode in which it is operating. This means that the pixel configuration of the LCD panel does not always agree with that of the video format in which the LCD panel receives images. For example, this happens when an XGA-type LCD panel receives SVGA- or VGA-format images, or when an SVGA-type LCD panel receives VGA-format images.
In such cases, a blank area appears on the screen of the LCD panel, and the screen therefore looks unnatural. To avoid this, Japanese Laid-open Patent Application No. H7-191630 discloses a method of filling the blank area with a particular color (e.g. black). Specifically, according to this method, false image data of a particular color is written to the blank area on the LCD panel through high-speed image data processing performed during the blanking intervals of the input video signal, whereas the real image data is written to the image area at the normal speed. As a result, a background of that particular color is displayed around the image area.
However, in this conventional method, the blank area needs to be filled with the particular color anew every time the screen (i.e. frame) is refreshed. This wastes processing time, requires high-speed processing, and therefore necessitates extremely efficient circuitry. In particular, this conventional method is especially disadvantageous in that it requires the dot clock to be switched in the middle of scanning between a high-speed dot clock for the blank area and a normal-speed dot clock for the image area. In addition, conventional LCD apparatus generally suffer from noticeable flickers in displayed images.